OBOLIDiE. 465 



do not know of any other large brachiopod of this type from the Cambrian or Ordovician rocks. 



The reference to the Lower Ordovician is made by reason of the presence of this Lingulobolus. 



The specific name is given for Mr. W. B. Rogers, v/ho first called attention to the species. 



Formation and locality. — lower Ordovician : (336) Liraestone pebbles on the beach, on the northern shore of 

 I.Iarthas Vineyard; and (326a [Grabau, 1900, p. 613]) limestone pebbles in a Carboniferous conglomerate north of Fall 

 River, Bristol County; both in Massachusetts. 



(343 [Rogers, 1875, p. 11, and U. 8. Nat. Mils.]) Limestone pebbles on the beach near Neioport and at several points 

 along the shores of Narragansett Bay, Rhode Island. 



(114h) Sandstone 1 mile (1.6 km.) north of Lance Cove, Great Belle Island, Conception Bay, Newfoundland. 



Obolus (Westonia) stoneanus (Whitfield). 

 I. 



Plate XXVIII, figures 2, 2a-g; Plate XLIX, figures 2, 2a. 



Lingula aurora var. Hall, 1863, Sixteenth Ann. Kept. New York State Cab. Nat. Hist., pp. 127-128, PL VI, figs. 6-8. 



(Described and discussed.) 

 Lingula aurora var. Hall, 1867, Trans. Albany Inst., vol. 5, pp. 104-106, PL I, figs. 6-8. (Copy of preceding reference.) 

 Lingulella aurora var. Hall, 1873, Twenty-third Ann. Rept. New York State Cab. Nat. Hist., pp. 244-245, PI. XIII, 



fig. 5. (Mentions change of genus. Fig. 5 is drawn from the same specimen as Hall, 1863, PL VI, fig. 7.) 

 Lingulella stoneana Whitfield, 1882, Geology of Wisconsin, vol. 4, pp. 344r-345, PL XXVII, figs. 6 and 7. (Charac- 

 terized and discussed as a new species.) 

 Lingulella stoneana 'WTiitfield, Hall and Clakke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, PL II, figs. 



9-11. (No text reference. Figs. 9 and 11 are copied from Hall, 1863, PL VI, figs. 7 and 8, respectively; and 



fig. 10 from Hall, 1873, PL XIII, fig. 5.) 

 Lingulella stoneana Whitfield, Wellee, 1903, Geol. Survey New Jersey, Eept. Paleontology, vol. 3, p. 112, PL I, fig. 6. 



(Described and discussed. The specimen represented by fig. 6 is redra^vn in this monograph, PL XLIX, 



figs. 2 and 2a.) 

 Obolus (Westonia) stoneanus (Whitfield), Walcott, 1901, Proc. U. S. Nat. Mus., vol. 23, p. 691. (Merely changes 



generic reference.) 



In form Obolus (Westonia) stoneanus (PI. XXVIII) approaches quite closely to the more 

 rounded shells of Lingulella amjAa (Owen) , except that in the dorsal valve the posterior lateral 

 slopes are broadly rounded, giving a subelliptical outline to the valve. The original convexity 

 of the valves is not presei'ved, but it appears to have been moderate, like that of Lingulella 

 ampla. A large ventral valve from Prairie du Sac has a length of 15 mm., with a maximum 

 width of 11 mm. An associated dorsal valve, 10 mm. wide, has a length of 11.5 mm. The 

 surface of the shell is strongly characteristic. It is formed by very fine concentric lines or strife of 

 growth crossed transversely by strong, undulating slightly lamellose lines (PL XXVIII, fig. 2d, 

 and PI. XLIX, fig. 2a). The margins of the inner surface of the shell show fine radiating lines. 

 All of the large number of specimens in the collection are flattened in the shaly sandstone, and 

 there is usually little left of the substance of the shell to afford a basis for an opinion of the 

 form or thickness. A careful study of the material, however, leads to the conclusion that the 

 valves were moderately convex and comparatively thin. In casts of the interior the concentric 

 strise and transverse lamellose lines are ahnost invariably strongly marked, and no traces of 

 the interior muscle scars or markmgs are preserved. 



The area of the ventral valve, as seen in a cast, is divided midway by the cast of the strongly 

 marked pedicle groove and, on each side and well out toward the margin, by the flexure lines. 

 The few strise of growth presei'ved cross the area parallel to its base. On the dorsal valve the 

 area is short, broad, and slightly arched forward near the center; the flexure lines are fairly 

 well preserved in a compressed cast of the shell. No muscle scars or vascular markings have 

 been observed on the interior casts of the ventral valve. A dorsal valve shows the central 

 muscle scars (h) and the base of the main vascular sinuses (vs) (PL XXVIII, fig. Ih). 



Observations. — This species was separated as a variety of Obolus (Westonia) aurora by 

 Professor Hall [1863, p. 127]. Later [18S2, p. 344], Professor Wliitfield, finding that its pecu- 

 liarities persisted in specimens found at localities where 0. (W.) aurora did not occur, gave it 

 a specific name. The peculiar surface ornamentation clearly distinguishes it from other species 

 62667°— VOL 51, ft 1—12 30 



